In the past few weeks I made some developments on the alternative solutions.
First I made a hardware decoder for timecode signal, which eliminates the analog audio processing in software or firmware. And I also added an external I2S DAC to the system to be able to use and test all 4 channels of audio. Here is a video of the new hardwarare unit. It is still the MIDI controls the iPad application but the midi signal is made directly from the vinyl audio.